A control method for controlling a hot strip rolling line,                wherein the hot strip rolling line comprises a finishing train for rolling flat rolling stock made of metal,        wherein the finishing train has a plurality of roll stands, through which the flat rolling stock passes in succession in a direction of passage,        wherein the hot strip rolling line comprises a cooling section disposed downstream of the finishing train,        wherein an initial value characterizing the energy content of the respective rolling stock point is determined for rolling stock points of the flat rolling stock at the latest when the respective rolling stock point enters the finishing train,        wherein the initial values are fed to a model for the hot strip rolling line,        wherein the rolling stock points are tracked as they pass through the finishing train and the cooling section,        wherein the trackings and energy content influences, to which the rolling stock points are subject in the finishing train and the cooling section, are also fed to the model,        wherein the control computer uses the model to determine expected values for the rolling stock points characterizing the current energy content of the rolling stock points passing through the hot strip rolling line continuously and in real time based on the initial values, the trackings and the energy content influences as the rolling stock points pass through the hot strip rolling line.        
Such subject matter is generally known. Reference is made purely by way of example to DE 101 56 008 A1 and the corresponding U.S. Pat. No. 7,197,802 B2.
A similar disclosure content is known from EP 2 301 685 A1. In EP 2 301 685 A1 the temperature of the corresponding rolling point can be detected by a measuring device to determine the initial value characterizing the energy content of the respective rolling point. The temperature progression over the thickness of the rolling stock can be determined by way of a model. A target energy content progression can also be determined and is taken into account when determining the energy content influences, to which the respective rolling stock point is subject.
The known control method operates very effectively when relatively thin strip material is rolled, so that all the roll stands of the finishing train engage, in other words roll the flat rolling stock (generally strip).
Relatively thick strip (known as tubular stock) with final rolling thicknesses of approx. 5 mm to approx. 30 mm is also rolled in finishing trains and the downstream cooling section. In this case rolling to the final rolling thickness must take place in a roll stand of the finishing train, which is not the last roll stand of the finishing train, for example the penultimate or third to last roll stand of the finishing train. The flat rolling stock passes through the following roll stands, in other words according to the example the last roll stand or the last and penultimate roll stands, without being rolled.
For the production of tubular stock it is necessary, in order to achieve favorable material properties—in particular high levels of viscosity and strength even at low ambient temperatures—to start cooling as early as possible and to cool quickly. If the flat rolling stock only starts to be cooled when it enters the cooling section disposed downstream of the finishing train, a relatively long time elapses between the end of rolling and the start of cooling. This has a negative influence on the achievable material properties of the flat rolling stock.
For this reason in the related art tubular stock is usually rolled in reversing mills. Reversing mills only have one roll stand, sometimes also two. The flat rolling stock is rolled in a reversing manner in the reversing mill. Cooling starts immediately after the last rolling pass.
If the finishing train has inter-stand cooling facilities, it is possible to start cooling the flat rolling stock immediately after the last rolling pass, so that in principle high quality tubular stock can also be produced in a multi-stand hot strip rolling line. Attempts have recently been made to do this. However in practice the following problem arises:
In the related art the temperature of the flat rolling stock is measured between the finishing train and the cooling section at a temperature measuring point. The measured temperature value is used to determine a—temporal or spatial—target energy content progression for the corresponding rolling stock point. The target energy content progression is used to determine the energy influences to which the corresponding rolling stock point is subject in the cooling section. However the intensive cooling by the inter-stand cooling facilities means that the surface of the flat rolling stock is cooled significantly. After the relevant inter-stand cooling facility the heat must be transferred back to the surface of the flat rolling stock by heat conduction from its interior. The relatively large thickness of the flat rolling stock means that this takes a relatively long time. The temperature state in the flat rolling stock is therefore not yet equilibrium at the temperature measuring point downstream of the finishing train. The temperature measurement downstream of the finishing train is therefore not usable. This has a negative influence on the accuracy with which the reeling temperature downstream of the cooling section can be set and maintained.
It may be possible to apply an offset to the measured temperature measurement value and thus achieve a roughly correct target energy content progression but this procedure is associated with considerable uncertainty and inaccuracy.